In the context of QA, there are multiple notions of explanation/justification,
including showing an authoritative, answer-bearing sentence [1]},
an attention map over a passage [2]}, a synthesized phrase
connecting question and answer [3]}, or the syntactic pattern
used to locate the answer [4]}, [5]}.
These methods are primarily designed for answers to “lookup” questions, to
explain where and how an answer was found in a corpus.
